1. Field of the Invention
The invention relates to thread-oriented processing and, in particular, to multiple-thread processing by the use of contexts.
2. Description of Related Art
In multiple-thread processing, a processor is capable of successively performing a plurality of different processes (commonly referred to as "threads"). Upon the occurrence of a particular event, such as after the elapse of a predetermined time period or upon the receipt of a specific command, the processor suspends performance of one thread, stores a context describing the status of the thread being suspended, and begins performing another thread, which is also described by a respective context. Each "context" describes information needed for the processor either to initiate operation on a new thread or to continue operation on a suspended thread. Typically this information identifies memory addresses containing the initial or next operation of a respective thread to be performed and any data to be operated on.
In order to provide direct and rapid access to stored thread contexts, some processors include multiple banks of local context registers. This, however, is an inflexible arrangement which limits to a fixed quantity the number of threads that can be performed. It is also inefficient whenever the number of threads is smaller than the number of register banks provided.
Alternatively, the multiple contexts can be stored in a separate memory. Various examples of such an approach are described in U.S. Pat. No. 5,349,680. In one of these examples, described in the patent as a conventional information processing apparatus, a main processor includes both an application supporting unit for successively performing operations from different application processes and a system supporting unit for controlling the operation in the information processing apparatus. The efficiency of this arrangement is described as inferior, because the application supporting unit and the system supporting unit are never operated at the same time. U.S. Pat. No. 5,349,680 proposes alternative arrangements utilizing multiple stored contexts, but each of these arrangements requires the use of two separate processors. This is an expensive way to improve efficiency.